Ball milling apparatus



Oct. 23, 1962 c. J. BENNING BALL MILLING APPARATUS Filed May 24, 1960 INVENTOR CALVIN J. BENNING Filed May 24, 1960, Ser. No. 31,481 1 Claim. (Cl. 23289) The device of this invention is a means for ball milling catalysts or the like under pressure of a reactive gas. In brief, the invention contemplates the addition of an auxiliary gas cylinder connected to the ball mill and adapted to roll with the mill on the same rollers during the milling operation. In normal operation, the connection between the gas cylinder and the ball mill is opened from time to time to maintain the gas pressures in the mill at a predetermined level. If the mill is small the assemblage of mill and auxiliary pressure vessel can be lifted manually off the rolls, gas admitted through the cut-off valve linking the gas cylinder and the mill, and the assemblage then returned to the rolls. If the mill is large, the rolls can be stopped to permit opening the valve. Under certain reaction conditions, it may be found desirable to leave the connecting valve open slightly during the milling operation so that admission of gas will be continuous during the milling operation.

The drawing shows a perspective view of the milling assembly. 1 and 2 are the rolls. The means for driving them is not shown. The mill is shown at 3; under normal operation it may be about /3 full of stainless steel balls. The mill 3 is provided with shut-ofi valve, 4, connected through the coupling 5 to the adjacent cutofi valve 6 of the gas cylinder 7. If the diameter of the gas cylinder is smaller than that of the mill, an adapter ring 8 may be fitted around it. Conversely, an adapter ring may be fitted around the mill if its diameter is smaller than that of the gas cylinder. If desired, the gas cylinder may also be fitted with charging or venting valve 9. It is not absolutely necesary to have both cut-off valves 4 and 6, but if both are present it is possible to seal ofi both the mill and the gas cylinder at the end of the run and disconnect and store both separately without loss of material.

It is "known to treat material being ground with a gas. See for example, U.S. 1,453,057, disclosing grinding iron oxide in the presence of a stream of hydrogen to make metallic iron.

It is also known to rotate together two or more interconnected mills in a ball-milling operation, as taught, for example, in U.S. 1,435,930, for grinding mixtures of salt and nitre cake, or U.S. 42,257, for grinding coal.

It is also known to ball mill catalysts under pressure in a single milling vessel. See U.S. 2,891,043. Further, in U.S. 2,856,272, polymer is made in situ by ball-milling the catalyst and monomer together under pressure.

It is also known to charge fluid material (liquid or vapor) through a stationary tube into a rotating ball mill, as shown in U.S. 955,814. However, such devices must generally provide elaborate cooling means to dissipate the frictional heat generated around the seal, and the problems of excluding ground material and vapor from the seal are difficult to deal with in practice.

The following examples illustrate the use of the invention.

Example 1 Here the apparatus is used to increase the activity of TiCl for use as a polyethylene catalyst. This is done by ball-milling the TiCl for a prolonged period under a predetermined pressure of ethylene gas. (This feature tent O is shown in more detail in copending Serial No. 786,758 filed 1-13-59, owned by the same assignee and now abandoned.)

To carry out this activation, a 750 ml. stainless steel mill 3 containing %-inch stainless steel balls and a charge of 173 g. TiCl was connected through two needle valves 4 and 6 to ethylene cylinder 7 having a capacity of 75 ml. and which contained ethylene under a pressure of 200 p.s.i.g. Both valves 4 and 6 were opened for a few minutes to equalize the pressure between the mill 3 and the ethylene cylinder 7. This gave a pressure of about 50 p.s.i.g. in the mill 3. The valves 4 and 6 were then closed and milling was begun. About every 4 to 6 hours the assemblage was removed from the rolls and the valves 4 and '6 opened to admit more ethylene to the mill 3 and then closed and milling resumed. This procedure was continued for three days, after which the nearly empty cylinder 7 was replaced by another (pressured at 30 0 p.s.i.g. of ethylene) and the procedure repeated for another day of milling. An additional cylinder charge of 400 p.s.i.g. ethylene was added intermittently on the beginning of the fifth day of milling, and the milling was finally stopped at the end of the fifth day. At this point the mill was disconnected from the cylinder by uncoupling the connector 5 (both valves 4 and 6 closed) and then opened in a nitrogen atmosphere to vent ofi a slight pressure of residual ethylene. The ethylene-activated TiCl catalyst was then removed and weighed. It showed a gain of 6.3 grams.

There are several advantages in the apparatus used as above described. The first and perhaps main advantage is the saving of time in pressuring the mill with active gas. In the old way, the mill had to be taken from the rolls, brought to the gas cylinder, connected to it, pressured, disconnected, and returned to the rolls, and this had to be done many times. In the new way as provided by my invention, the connection to the gas cylinder is semi-permanent, and very little time is lost. Even the act of replacing the cylinder 7 is less time consuming than one repressuring by the old technique.

Example 2 The apparatus was used in such a way to provide a predetermined weight of active gas (in this case, hydrogen) to the catalyst being milled, but at a pressure not exceeding substantially atmospheric pressure, and by use of a technique not requiring removal of the mill from the rolls except at the end of the run.

In this particular run it was desired to add 0.3 g. (0. 15 mole) of hydrogen to a mixture of aluminum turnings (16 g.) and TiCl (30 g.) at a uniform rate over a hour period of uninterrupted ball milling, so as to prepare a highly active polyethylene catalyst. (The preparation and use of this catalyst is described in more detail in copending Serial No. 825,410, filed July 7, 1959, owned by the same assignee.)

To accomplish this, the gas cylinder 7 was first pressured with hydrogen to about 60 p.s.i.g. This cylinder was then placed in a pneumatic trough and the valve 6 opened slightly. The bubbles coming oil were collected and measured. The valve was adjusted until the hydrogen flow rate was 0.5 ml. per minute (equal to 0.3 g. over the projected 5 day run).

The mill 3, containing the A1-TiC1 mixture and about /3 its volume of steel balls, was flushed with nitrogen and connected to the gas cylinder 7, with valve 4 fully open and valve 6 adjusted as above described. The thus-assembled mill and cylinder were then placed on the rolls, and the milling operation was begun and continued without interruption for 5 days. At the end of this time, the run was stopped and the catalyst recovered 3 as above described. The hydrogen pick-up was very nearly 0.3 g.

For situations in which moisture or foreign liquids cannot be tolerated near the mill, or if it be desired to keep the mill asesmbly completely intact, the center connecting tube or coupling 5 can be replaced by a small gas regulator (not shown) of any well known design. Such gas regulator (calibrated before installation) will deliver a steady stream of any gaseous product and thereby avoid the calibration step and associated technique in Example 2.

I claim:

In apparatus for milling catalysts and the like under pressure of a reactive gas, the combination consisting of a set of parallel mill-driving rolls, power means to rotate the rolls, a pressure-resistant ball-mill having a cylindrical body, a container for compressed, reactive gas comprising a cylinder having a diameter other than that of the mill, an adaptor ring fitted about the smaller of the cylindrical bodies to increase its effective diameter to that of the larger cylinder, the cylindrical wall of one of said cylinders and the cylindrical wall of the adaptor ring resting upon and being rotatable by said rolls, a conduit extending between the mill and the gas cylinder centered on the longitudinal axis and providing a gas passage interconnecting the interior of the mill with that of the cylinder, and valve means in the conduit adapted to control the volume of gas supplied to the mill, whereby both cylinders may rotate as a completely sealed unit about a common axis and pre-determined gaseous conditions may be uninterruptedly maintained in the mill throughout the duration of a mill run.

References Cited in the file of this patent UNITED STATES PATENTS 520,205 Heylingstaedt May 22, 1894 955,814 Leet Apr. 19, 1910 1,435,930 Laury Nov. 21, 1922 1,453,057 Williams Apr. 24, 1923 1,862,557 Wendler June 14, 1932 1,879,479 Punnett Sept. 27, 1932 2,856,272 Baeyaert Oct. 14, 1958 

